1. Field of the Invention
The present invention relates generally to devices for treatment of hyperproliferative tissues, and more particularly to a system and method for the treatment of benign prostate hyperplasia that substantially simultaneously ablates excess tissue and coagulates tissue just beyond the ablation, providing a near blood-free treatment, by utilizing at least two or more separate wavelengths of light.
2. Information Disclosure Statement
Benign prostatic hyperplasia (BPH) or “enlarged prostate” refers to the noncancerous (benign) growth of the prostate gland. While BPH is the most common prostate problem in men over 50 years of age, benign growth of the prostate begins with microscopic nodules around 25 years of age but rarely produces symptoms before a man reaches 40. It is estimated that 6.3 million men in the United States have BPH and the disease is responsible for 6.4 million doctor visits and more than 400,000 hospitalizations per year.
The exact cause of BPH is unknown but it is generally thought to involve hormonal changes associated with the aging process. Testosterone likely has a role in BPH as it is continually produced throughout a man's lifetime and is a precursor to dihydrotestosterone (DHT) which induces rapid growth of the prostate gland during puberty and early adulthood. When fully developed, the prostate gland is approximately the size of a walnut and remains at this size until a man reaches his mid-forties. At this point the prostate begins a second period of growth which for many men often leads to BPH later in life.
In contrast to the overall enlargement of the gland during early adulthood, benign prostate growth occurs only in the central area of the gland called the transition zone, which wraps around the urethra. As this area of the prostate grows, the gland presses against the urethra and causes a number of lower urinary tract symptoms (LUTS) such as difficult urination (obstructive symptoms) and painful urination (storage symptoms). Eventually, the bladder itself weakens and loses the ability to empty itself.
Obstructive symptoms such as intermittent flow or hesitancy before urinating can severely reduce the volume of urine being eliminated from the body. If left untreated, acute urine retention can lead to other serious complications such as bladder stones, urinary tract infections, incontinence, and, in rare cases, bladder damage, kidney damage. These complications are more prevalent in older men who are also taking anti-arrhythmic drugs or anti-hypertensive (non-diuretic) medications. In addition to the physical problems associated with BPH, many men also experience anxiety and a reduced quality of life.
Mild symptoms of BPH are most often treated with medication such as alpha-blockers and anti-androgens. Men suffering with moderate to severe BPH symptoms typically must undergo surgery. Transurethral resection of the prostate (TURP) is the standard surgical procedure, although there are a number of other surgical approaches available as well. Other less invasive surgical methods include: transurethral incision of the prostate (TUIP), transurethral microwave thermotherapy (TUMT), transurethral electro vaporization (TUVP), transurethral needle ablation (TUNA), and laser surgery.
There are a number of different laser techniques in which light is used to eliminate excess prostate tissue either by ablation (vaporization) or thermal coagulation mechanisms. The observed clinical effects are due to the absorption of light (by the target tissue itself and/or surrounding fluids) and subsequent heat transfer, the extent of which largely depends on the power and wavelength of the laser beam. In general, wavelength determines the depth of tissue penetration while power has a direct influence on the temperature created within the tissue. However, it is temperature that determines the ultimate impact at the treatment area since tissue must be heated to greater than 50 C to induce coagulation whereas vaporization occurs at temperatures over 100 C. Temperature also impacts morbidity, namely inflammation, dysuria, bleeding, and the need and duration of post-treatment catheterization.
Laser approaches currently in use for the treatment of BPH utilize a single wavelength of light to eliminate excess prostate tissue via ablation or by inducing coagulation necrosis. Initially, however, laser surgeries for BPH used the holmium: YAG laser in combination with the Nd:YAG laser in a treatment method called Combination Endoscopic Laser Prostatectomy (CELAP) being a two step process where the holmium laser was used to create the channel through the prostate and the Nd laser was used for coagulation. It was further determined that the Nd laser was unnecessary if the holmium laser was defocused for coagulation purposes. See A. H. H. Tan and P. J. Gilling, Holmium Laser Prostatectomy, BJU International, 92, 527-530 (2003). For the CELAP procedure, the holmium laser was used to create a channel in the prostate by vaporizing the tissue after which, the Nd:YAG laser was used to further eliminate tissue via coagulation. CELAP has been replaced by newer, single-wavelength laser methods which are still being evaluated for long-term efficacy.
Holmium Laser Enucleation of the Prostate or HOLEP is a laser ablation technique in which a 2140 nm Ho:YAG laser is used to remove whole lobes from the prostate. Specifically, HOLEP uses a bare optical fiber which is brought into direct contact with the target tissue. Enucleation occurs when the vapor bubbles that form in front of the fiber bombard the target tissue and tear it apart. Special morcellators or other extraction techniques are needed to remove tissue debris from the area. The efficacy of the HoLEP procedure depends upon maintaining very close contact between the fiber and the tissue to be removed. As a result, it is possible to perforate the prostate during the procedure and many surgeons avoid using HoLEP because of the difficulty in learning and maintaining proficiency in the technique.
Another laser technique to eliminate prostate overgrowth features a frequency-doubled Nd:YAG laser as a pulsed, 532 nm high-power potassium-titanyl-phosphate laser (KTP) that vaporizes target tissue as well as induces thin layers of coagulation in the surrounding tissues as described by Davenport et al. in U.S. Pat. No. 6,554,824. The 532 nm radiation used in KTP is selectively absorbed by hemoglobin and penetrates tissues only to a depth of 1-2 mm. Moreover, this method requires continuous irrigation of the treatment site to cool the tissue during the procedure to help reduce unwanted coagulation necrosis in deeper tissue layers.
Interstitial laser coagulation (ILC) is a minimally invasive method that uses a Nd:YAG laser to reduce the volume of the prostate by inducing coagulation necrosis in the interior of the prostate, as opposed to eliminating tissue via ablation. As a result, ILC does not require the removal of tissue debris during treatment and avoids subsequent sloughing (and associated bleeding) of necrotic tissue post-treatment. However, this wavelength has a relatively long penetration depth and thus has the capacity to produce deeper and broader zones of thermal damage there as necessary. As such, ILC treatment methods require precise, well-controlled positioning and monitoring of the laser fiber tip during the procedure and may only be appropriate for a select group of patients (i.e. patients having a specified pre-operative prostate volume).
Much like TURP, most types of laser surgeries are able to provide an immediate improvement in the urinary stream. Laser surgery for BPH has other potential advantages such as reduced blood loss as well as shorter treatment times, faster patient recovery, and a lower risk of post-treatment incontinence. However, many patients still require catheterization for 1-2 weeks post-treatment after undergoing some forms of laser surgery. Despite the obvious benefits of laser procedures for BPH, long-term follow-up studies on the clinical results of many laser techniques are not yet widely available.
To date, none of the less invasive procedures have proven to be more effective than TURP nor are they generally appropriate across all patient groups including: younger men, debilitated elderly patients, patients with severe medical conditions including uncontrolled diabetes, cirrhosis, active alcoholism, obesity, and heart disease, as well as men taking blood thinning medications. As such, there remains a need for a device and treatment method for the effective alleviation of BPH symptoms that can be used across all patient groups with a minimum of adverse complications post-treatment. The present invention is directed towards this need.